Shelf



FIG. 1 is a front perspective view of a shelf embodying the principles of our new design;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a top view thereof, the bottom view being a mirror image thereof; and,

FIG. 5 is a side view thereof, the opposite side being a mirror image thereof.

The broken line showing of hanging elements in FIGS. 3, 4 and 5 form no part of the claimed design. 

The ornamental design for a shelf, as shown and described. 